Profound Impact of Decline in N-Acetylgalactosamine-4-Sulfatase (Arylsulfatase B) on Molecular Pathophysiology and Human Diseases

Abstract

The enzyme N-acetylgalactosamine-4-sulfatase (Arylsulfatase B; ARSB) was originally identified as a lysosomal enzyme which was deficient in Mucopolysaccharidosis VI (MPS VI; Maroteaux-Lamy Syndrome). The newly directed attention to the impact of ARSB in human pathobiology indicates a broader, more pervasive effect, encompassing roles as a tumor suppressor, transcriptional mediator, redox switch, and regulator of intracellular and extracellular-cell signaling. By controlling the degradation of chondroitin 4-sulfate and dermatan sulfate by removal or failure to remove the 4-sulfate residue at the non-reducing end of the sulfated glycosaminoglycan chain, ARSB modifies the binding or release of critical molecules into the cell milieu. These molecules, such as galectin-3 and SHP-2, in turn, influence crucial cellular processes and events which determine cell fate. Identification of ARSB at the cell membrane and in the nucleus expands perception of the potential impact of decline in ARSB activity. The regulation of availability of sulfate from chondroitin 4-sulfate and dermatan sulfate may also affect sulfate assimilation and production of vital molecules, including glutathione and cysteine. Increased attention to ARSB in mammalian cells may help to integrate and deepen our understanding of diverse biological phenomenon and to approach human diseases with new insights.

Keywords: Arylsulfatase B; N-acetylgalactosamine-4-sulfatase; Warburg effect; chondroitin 4-sulfate; cystic fibrosis; dermatan sulfate; malignancy; mucopolysaccharidosis; proteoglycans; sulfated glycosaminoglycans.

Figure 1

Representative images of normal and malignant prostate cancers, immunostained for ARSB. (A–E). Declines in intensity and in membrane immunostaining are evident, as Gleason score increases from 6 to 9 [42].

Figure 2

ARSB immunostaining of malignant and non-malignant human colonic epithelial cell lines. The malignant T84 cells (A) have markedly lower immunohistochemical intensity than the NCM460 cells (B). Cell membrane immunostaining is prominent in the non-malignant cells [34].

Figure 3

Fluorescent immunostaining of ARSB in human cerebrovascular cells. (A,B). Confocal microscopy demonstrates cell surface localization of ARSB in untreated cerebrovascular cells, as well as cytoplasmic and nuclear localization and presence of ARSB in cell projections. ARSB is stained red, and β-actin is stained green [44].

Figure 4

Mechanisms leading to impaired cell signaling and transcriptional events. Decline in ARSB leads to accumulation of chondroitin 4-sulfate and dermatan sulfate. Decline in ARSB may be due to congenital mutation, hypoxia, increased exposure to chloride or phosphate, estrogen, ethanol, carrageenan, or other exposures, as indicated in Table 2 and Section 4. The signaling pathways were explored with chondroitin 4-sulfate (C4S), since a C4S antibody which detected C4S chains was available. Two major pathways are affected by increased C4S, as shown. Galectin-3 binds less to more highly sulfated C4S and becomes available for other interactions, including increased binding with the insulin Receptor, leading to inhibition of insulin signaling [80,81,82] and increased binding with transcription factors, enabling increased DNA binding and transcriptional effects [27,32,33,34,35]. In contrast, SHP2 binds more with C4S when ARSB is silenced, leading to reduced phosphatase activity [14,28,33,36,37,38] and sustained phosphorylation of critical signaling molecules, including phospho-ERK1,2 [33,36,83], phospho-JNK [28], and phospho-p38 MAPK [14,38]. Due to the complexity of the phospho-proteome, the manifestations of sustained phosphorylations impact multiple signaling events. These include increased c-Myc activation of DNMTs and increased methylation of DKK3, which when active acts as an inhibitor of Wnt signaling [36,37,38].

Figure 5

Overall schematic of transcriptional effects following decline in ARSB. Decline in ARSB leads to increase in chondroitin 4-sulfation, due to failure to remove the sulfate group at the non-reducing end and inhibition of degradation, as occurs in the inherited disorder MPS VI. Increased binding to C4S occurs for several vital molecules, including IL-8 [29] and BMP-4 [30]. Sequestration of IL-8 in the cell membrane can lead to increased neutrophil chemotaxis and contribute to impaired mucociliary clearance. BMP4 retention with C4S can alter Wnt-BMP interactions and reduce the Smad-mediated expression of CHST11 [30], thereby impairing production of new C4S. Galectin-3 binds less to more highly sulfated C4S, leading to availability for binding with the insulin receptor, and thereby contributing to insulin resistance [80,81,82]. In addition, galectin-3 acts as a co-transcriptional activator, combining with AP-1 and Sp1 for enhanced transcription of versican [37], CSGP4 [33], HIF-1α [35], Wnt9A [32], and PD-L1 [85]. In contrast, SHP2 binds more with C4S when ARSB is inhibited, leading to decline in phosphatase activity and sustained phosphorylation of important mediators, including phospho-ERK [33,36,83], phospho-JNK [28], and phospho-P38 MAPK [14,38]. Through a network of signaling events, nuclear c-Myc [36] and MITF [14] and other transcription factors act to increase expression of pro-MMP2 [33], MMP9 [33,83], GPNMB [14], EGFR [28], and DNMT1 and 3a [36]. Hence, a broad range of vital cellular processes are regulated due to changes in ARSB activity and chondroitin-4 sulfation.

Figure 6

Predominant effects of decline in Arylsulfatase B (ARSB) in mammalian cells. Decline in ARSB leads to profound effects on vital cell processes in mammalian cells, as indicated in this report. C4S = chondroitin 4-sulfate; DS = dermatan sulfate; EMT = epithelial-mesenchymal transition; CHST = chondroitin sulfotransferase; ERK = extracellular-signal regulated kinase; MAPK = mitogen- activated protein kinase; JNK = c-Jun N-terminal kinase; SHP2 = tyrosine-protein phosphatase non-receptor type 11.